Acute respiratory distress syndrome (ARDS) is a complex, multi-factorial syndrome which manifest itself by leaky lung microvessels, protein rich edema, and intractable hypoxemia. Given that recent studies from both human and animal studies has demonstrated the key role of microvascular leakage in determining the outcome of sepsis and ARDS, maintaining the endothelial barrier integrity represents a novel, effective therapeutic approach for the prevention and treatment of ARDS. However, the molecular mechanisms mediating endothelial barrier disruption after sepsis remain poorly understood, especially, little is known about the key molecules and signaling pathways responsible for endothelial barrier dysfunction resulting in high mortality in ARDS patients. Our Supporting Data show that higher levels of plasma SDF1 in ARDS patients are positively associated with high mortality. In mice, we observed that SDF1 treatment augmented sepsis-induced lung injury and mortality, which were attenuated in mice with inducible EC-specific disruption of Cxcr4 (Cxcr4iEC). Importantly, our mechanistic studies demonstrate that SDF1 treatment induces endothelial cell pyroptosis leading to severe endothelial barrier dysfunction. Thus, we hypothesize that elevated plasma SDF1 levels is a prognostic biomarker of severe lung injury and greater mortality of ARDS patients which is ascribed to SDF1-induced overwhelming endothelial pyroptosis and resultant severe endothelial barrier dysfunction following sepsis. The proposed studies will address the following Specific Aims. Studies in Aim 1 will validate circulating SDF1 level as a prognostic biomarker of ARDS patients and define the signaling pathway mediating SDF1-exaggerated lung injury and mortality following sepsis challenge. Studies in Aim 2 will delineate the molecular and cellular mechanisms of SDF1 in augmenting sepsis-induced lung injury through activation of endothelial pyroptosis and explore the therapeutic potential of inhibiting pyroptosis for treatment of ARDS. With the data from these comprehensive studies, we will delineate the fundamental mechanisms of endothelial injury, identify a prognostic biomarker for the severity and mortality of ARDS, and provide novel therapeutic approaches for effective treatment of ARDS and promotion of survival. Thus, these innovative mechanistic studies have high translational potential.